System and methods for bilirubin analysis

ABSTRACT

A method for measuring bilirubin levels in a subject. The method can include the steps of providing a sample to be measured from the subject, wherein the sample comprises bilirubin bound to albumin; adding a release agent to the sample, the release agent configured to release the bound bilirubin from the albumin; measuring electrochemical data of the sample using an electrochemical cell; and determining a total serum bilirubin concentration of the sample using the electrochemical data. This method is capable of providing a simpler, faster, and more robust measurement when compared to traditional bilirubin assay methods.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/374,234 filed Apr. 3, 2019 which is a divisional of U.S. applicationSer. No. 15/954,360 filed on Apr. 16, 2018 which claims the benefit ofU.S. Provisional Patent Application Ser. No. 62/552,226, filed on Aug.30, 2017, and entitled “SYSTEMS AND METHODS FOR JAUNDICE DETECTION.”

BACKGROUND

Neonatal jaundice is one of the most common physiological manifestationsin newborns; the illness presents itself in nearly 60% of term neonatesand in 80% of pre-term neonates. The illness is a primary reason forhigh re-admission rates because of its delayed onset. Jaundice isgenerally benign as its part of the physiological evolution process ofneonate's hepatic system, but incorrect or delayed diagnosis can lead tosevere brain damage, causing cerebral palsy or kernicterus. Accurateestimation of jaundice is essential for proper intervention and toprevent the development of jaundice into severe hyperbilirubinemia,especially with a growing number of babies being discharged early andsent home.

In the body, because of the large number of potentially reactive groupsin bilirubin, very little bilirubin exists free in circulation. Most ofthese derivatives rapidly associate with albumin, through a network ofreversible hydrogen bonds. Together, free- and albumin-bound bilirubinare referred to as unconjugated bilirubin also known as α-bilirubin.Unconjugated bilirubin on reaching the liver, is covalently conjugatedto glucuronic acid forming mono and diglucuronides (β and γ bilirubin)not bound to albumin, collectively known as conjugated bilirubin. Thewater-soluble bilirubin glucuronides are excreted through feces andurine, while a portion gets reabsorbed in duodenum contributing to theenterohepatic circulation. Note, irreversible binding can also occur,and it is now known that in some jaundiced patients' conjugatedbilirubin is present in the serum covalently bound to albumin. Thisspecies has been called δ-bilirubin.

Free bilirubin (unconjugated and unbound to albumin) is the suspected asbeing the only form in which bilirubin can cross the intact blood-brainbarrier. In clinical practice, the concentration of total bilirubin inneonates is usually equal to unconjugated bilirubin. Total bilirubin isused as an easily measured proxy for the concentration of unconjugatedbilirubin, and hence the risk of bilirubin induced neurotoxicity (BIND)or kernicterus. Although, excess levels of conjugated bilirubin andδ-bilirubin can cause conjugated hyperbilirubinemia and cholestaticjaundice, respectively, it's extremely rare in neonates. Unconjugatedhyperbilirubinemia is more common condition as it is a consequence ofphysiological development of the hepatic system.

Preventing newborns from toxic bilirubin levels has been one of theprime concerns for pediatricians. Currently tools like a nomogram, usedfor plotting hour specific total serum bilirubin levels vs. age ofnewborns, are employed to understand the trend of the blood bilirubinlevels and potential risk of developing hyper-bilirubinemia prior todischarge. Bhutani's nomogram is the industry standard and has beenrecommended by both AAP and NICE for the same purpose.

In current practice, using isolated risk factors as a measure to predictthe subsequent development of hyperbilirubinemia in early dischargednewborns has been largely unsuccessful. On top of that, transcutaneousbilirubin (TcB) measurement, used for screening neonates and preferredfor their noninvasiveness, can be confounded by the discrepanciesbetween total serum bilirubin (TB) and TcB values above 12 mg/dL (205mol/L), resulting in TcB nomograms that underestimate TB levels >12mg/dL (205 mol/L). Despite the numerous studies to improve jaundicediagnosis in the past 30 years, there has been a relapse inreadmissions, bilirubin encephalopathy, and kernicterus. These trendspoint towards the need, more than ever before, for improved diagnosticmethods, and to treat physiological conditions safely and comfortably inhome and hospital settings.

In the current liability-focused environment, hospitals have startedadapting cost containment strategies, such as managed care, resulting ina continued trend toward a shorter length of stay for patients. Earlydischarge has had a potential effect on the efficacy of neonatalscreening causing increased readmissions due to jaundice. Patient andprovider convenience is a contributing factor to the increasing rate oflate-preterm delivery.

Prompt and accurate estimation of bilirubin levels can help offset thedamage caused by readmission, but the laboratory techniques used inhospitals have several deficiencies, listed below, that prevent themproperly managing the complications in neonates, especially jaundice.

A large contribution to error in any test results comes frompre-analytical errors and bilirubin tests are more sensitive: When asample is drawn there is no continued metabolism that will cause achange in the bilirubin concentration. However, it is well known thatbilirubin in a sample can be degraded by exposure to light, which isalso used as treatment of hyperbilirubinemia. Irradiation of a serumsample changes the structure of the bilirubin molecule into severaldifferent polar (water-soluble) photoproducts. Some studies have shownthat in vitro bilirubin may be degraded up to as much as 50% by lightdegradation. Additionally, the sampling site for bilirubin testing canresult in further discrepancies. Even though there is no agreement inthe literature as to whether there is any difference in relation to thechoice of sampling site, capillary sampling is preferred as it ensuresthat only small sample volumes are obtained to avoid iatrogenic anemia,but it also introduces additional pre-analytical factors.

One study reports that out of all the participating laboratories, over60% of laboratories are using the diazo diagnostic methods. The diazomethods come with numerous drawbacks, many of which stem from theinterference caused by other proteins present in the heme during directspectroscopic measurement as well as the pH dependency. Further, thereagents used with these methods can be troublesome to work with, oftenhaving poor stability and requiring several volume transfers, which maylead to inaccurate results. Additionally, the methods can be relativelyslow, often requiring 30 minutes or more to provide the total serumbilirubin measurement after initiation.

Other less popular methods include enzymatic methods, HPLC, and directspectroscopy, and each come with unique drawbacks. For example,enzymatic methods often use bilirubin oxidase which is hard toimmobilize, unstable, and rather expensive. Regarding HPLC, traditionalmethods use an assay setup that is expensive, bulky, and complex. Directspectroscopy methods often require dilutions in order to correct forinterference from hemoglobin, carotenoids, and turbidity. Additionally,direct spectroscopy cannot be automated and consequently is limited inclinical application. With the above technologies, the measurementapparatuses are difficult to minimize which has limited their abilitiesto provide point-of-care (POCT) testing for bilirubin.

The initiation of jaundice treatment depends on the bilirubin levels,which in previous laboratory tests, has required significant levels ofblood, has the risk of sample compromise, labor intensive, and timeconsuming. Although, jaundice is benign, as its part of thephysiological evolution process of neonate's hepatic system, incorrector delayed diagnosis could lead to severe brain damage like cerebralpalsy or kernicterus.

Operational inefficiencies in current clinical systems heavily revolvearound administrational activities in patient management. Progressivesteps towards tackling the situation can be addressed by embracing newtechnology in order to overcome pain points that include lack ofefficiency, avoidable admissions and readmissions, medical errors,defensive practice, communication, and excessive administrativeservices. Point of care technology is one of the many technologicaladvances that has the potential to reduce operational inefficiencies,improve the patient monitoring, and diagnostic accuracy. This isespecially true in the case of neonatal jaundice, where promptmanagement is essential to prevent disorders such as neurologicalinduced dysfunction (BIND) and kernicterus.

In short, total serum bilirubin is an important clinical measurement inhepatobiliary disorders and haematological disorders; the importance ofbilirubin is underlined by the numerous efforts to measure in a clinicalsetting including spectrophotometry, HPLC, fluorometry, and enzymaticmethods. As noted above, these methods have several disadvantages suchas excessive sample preparation, time-consuming analyses, interferences,and instability of reagents. Furthermore, these methods need to beperformed with consideration of the photosensitivity of the bilirubinwhich can critically underestimate bilirubin levels if not sampled inthe absence of light.

SUMMARY OF THE DISCLOSURE

The present disclosure addresses the aforementioned drawbacks byproviding systems and methods for electroanalytical measurement ofbilirubin in a sample from a subject. These systems and methods are ableto provide a simpler, faster, and more robust measurement when comparedto traditional bilirubin assay methods. The sample may be cooled,transported, prepared, and analyzed using a simple system, therebyeliminating the largest source of error caused by manual handling andsample preparation. The system has an extended shelf life, is easier touse, and is more economical than most of the previous bilirubin assays.The system and methods may be used to provide point-of-care testing ofbilirubin in a subject.

In one aspect, the present disclosure provides a method for measuringbilirubin levels in a subject. The method can comprise providing asample to be measured from the subject, wherein the sample comprisesbilirubin bound to albumin; adding a release agent to the sample, therelease agent configured to release the bound bilirubin from thealbumin; measuring electrochemical data of the sample using anelectrochemical cell; and determining a total serum bilirubinconcentration of the sample using the electrochemical data.

In another aspect, the present disclosure provides a method fordiagnosing a subject based on electrochemical detection of analytes. Themethod can comprise providing a blood sample to be measured from thesubject, wherein the sample comprises both unbound bilirubin andbilirubin bound to albumin; adding a release agent to the sample, therelease agent configured to release the bound bilirubin from thealbumin; measuring electrochemical data of the sample using anelectrochemical cell; determining concentrations of conjugatedbilirubin, unconjugated bilirubin, total serum bilirubin and albuminusing the electrochemical data; and making a diagnosis of an illness forthe subject based on the determined concentrations of conjugatedbilirubin, unconjugated bilirubin, and albumin

In yet another aspect, the present disclosure provides a system forelectrochemical detection of analytes. The system can comprise acartridge comprising a receiving zone configured to receive a sample,wherein the sample comprises bilirubin bound to albumin; a preparationzone holding a release agent and configured to receive the sample fromthe receiving zone and combine the sample with the release agent inorder to release the bound bilirubin from the albumin; and a sensingzone having multiple electrodes and configured to receive the samplefrom the preparation zone and provide electrical energy from theelectrodes to a connector. The system can also comprise a deviceconfigured to receive a portion of the cartridge, wherein the devicecomprises a receptacle configured to receive and be in electricalcommunication with the connector; a controller in electricalcommunication with the receptacle and configured to: control a potentialon at least one of the electrodes; and receive the electrical energy andprovide information regarding concentrations of analytes present in thesample.

The foregoing and other aspects and advantages of the present disclosurewill appear from the following description. In the description,reference is made to the accompanying drawings that form a part hereof,and in which there is shown by way of illustration a preferredembodiment. This embodiment does not necessarily represent the fullscope of the invention, however, and reference is therefore made to theclaims and herein for interpreting the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a flowchart of a method for measuring bilirubin levels ina subject, in accordance with one aspect of the present disclosure.

FIG. 2 depicts a flowchart of a method for diagnosing a subject based onelectrochemical detection of analytes, in accordance with one aspect ofthe present disclosure.

FIG. 3 depicts a system for electrochemical detection of analytes, inaccordance with one aspect of the present disclosure.

FIG. 4A depicts a perspective view of a cartridge to be used in a systemfor electrochemical detection of analytes, in accordance with one aspectof the present disclosure. FIG. 4B depicts a top view of the cartridge.

DETAILED DESCRIPTION

As used herein, “total serum bilirubin”, also referred to as “totalbilirubin”, is the union of conjugated and unconjugated bilirubin. Totalserum bilirubin level has been described as providing a generallyreliable measure of health of a person's hepatic system. Thus, it isoften one of the first metabolites measured to evaluate the health of aneonate regarding the risk of hyperbilirubinemia. The decision toinitiate phototherapy, or any other course of action regardinghyperbilirubinemia, is often based on the newborn's age and total serumbilirubin level and rate of change of total serum bilirubin level.

Conjugated bilirubin has glucuronic acid moieties that are not presentin unconjugated bilirubin. Conjugated bilirubin can be formed in theliver resulting from the hepatic conjugation of unconjugated bilirubinto make it water soluble. There are instances where a subject may havenormal levels of total serum bilirubin but excess conjugated bilirubinand δ-bilirubin (collectively called direct bilirubin). Hence,identifying these newborns with cholestasis from the masses of jaundicednewborns can be difficult but is important for early diagnosis andtreatment. For this reason, conjugated bilirubin levels are oftenmeasured.

This unconjugated form is suspected of being the only form of bilirubincapable of crossing the intact blood-brain barrier. The serum proteinalbumin binds to unconjugated bilirubin making it less toxic.

The total serum bilirubin (TSB), unconjugated bilirubin (B_(f)), albumin(A), and bilirubin binding capacity (K) are related through equation 1:

$\begin{matrix}{B_{f} = \frac{{TSB} - B_{f}}{K\left( {A - {TSB} + B_{f}} \right)}} & (1)\end{matrix}$

A common misconception in clinical practice is that the TSB andTSB/Albumin ratio (TSB/A) independently predict kernicterus. In fact,the current American Academy of Pediatrics guidelines for managinghealthy jaundiced term and near-term newborns recommends the use of theTSB/A ratio in addition to the TSB. While the ratio is a rough measureof bilirubin-albumin binding and has not been widely used clinically,clinicians have been recently encouraged to measure the albumin levelsalong with the TSB.

As used herein, a subject may be a living organism. The subject may be aliving organism with a liver. The subject may be mammalian. The subjectmay be a human. The subject may be a neonate.

Although the system and methods of the present disclosure are oftendescribed as being intended for use with neonates for diagnosingjaundice, one of skill in the art could envision could envision applyingthe teachings described herein to a variety of additional applications.

Described herein are systems and methods for electrochemical detectionof analytes such as bilirubin derivatives and albumin. In general,electroanalytical methods are used on a sample that has been treatedwith a release agent to release bound bilirubin from albumin.

FIG. 1 depicts a flowchart 100 of a method for measuring bilirubinlevels in a subject. The flowchart 100 comprises a first step 102 ofproviding a sample comprising bilirubin bound to albumin. The sample maybe a bodily fluid, tissue sample, or excretion from the subject. Forexample, the sample may be a blood sample of the subject. The bloodsample may be whole blood or separate blood. The sample may also beplasma, serum, or cerebral spinal fluid (CSF), Such a sample may betreated or untreated prior to being provided. The blood sample may beprovided within a short period of time after being acquired from thesubject, for example the blood sample may be provided within 60 secondsof being drawn from the subject. The blood sample may have a volume lessthan 100, 50, 40, 30, 20, 10, 7, 4, or 2 microliters or less.

The flowchart 100 comprises a second step 104 of adding a release agentto the sample, the release agent configured to release the boundbilirubin from the albumin. The release agent may release the boundbilirubin by means of competitive inhibition. The release agent mayrelease additional molecules bound to albumin that are not bilirubinderivatives. The release agent may be4,4′-(1,1-dioxido-3H-2,1-benzoxathiole-3,3-diyl)bis(2,6-dibromophenol),also referred to as bromophenol blue. Other suitable release agentsinclude, without limitation, cocoamidopropyl sulfobetaine, CHAPS(3-[3-Cholamidopropyl)-dimethylamminonio]-1-propanesulfonate), CHAPSO(3-[3-Cholamidopropyl)-dimethylamminonio]-2-hydroxy-1-propanesulfonate),cocoamidopropyl betaine, caffeine, sodium benzoate, sodium acetate,ethylene glycol, hexadecanoic acid, (9Z)-octadec-9-enoic acid, haematin,sulfonamides, salicylate, sodium dodecyl sulfate,4,4′-(1,1-dioxido-3H-2,1-benzoxathiole-3,3-diyl)bis(2,6-dibromophenol).The release agent may be in the form of a dry solid prior to being addedto the sample. Alternatively, the release agent may be formed as anon-dry solid or a fluid (e.g. a gas or a liquid). The amount of releaseagent may be dependent on the concentration of the sample and theexpected clinical range of bilirubin. For example, a 1 to 3 equivalentmolar concentration of the release agent relative to the upper limit ofthe expected clinical range of bilirubin may be used.

The sample may undergo additional treatments prior to the measurementstep. For example, the sample may be filtered to remove particles abovea certain size. Additional agents may be added to the sample. Theseadditional agents may include a surfactant, buffer, salt, second releaseagent, or mixtures thereof. If a surfactant is added, the surfactant maycomprise sodium dodecyl sulfate or CHAPS(3-[3-Cholamidopropyl)-dimethylamminonio]-1-propanesulfonate). If abuffer is added, the buffer may comprise a phosphate buffer ortris(hydroxymethyl)aminomethane. If a salt is added, the salt maycomprise sodium chloride, potassium chloride, sodium hydroxide, asimilar salt, or any combinations thereof. The second release agent maybe any component previously listed for the release agent. Theseadditional agents may be in the form of dry solids. The additionalagents and the release agent may be added to the sample sequentially. Inother words, the dissolution of these additional agents can be distinctor overlapping with respect to time. Because some agents could beintrinsically incompatible if formulated together or stored in directcontact, adequate physical separation may be needed in order to preventinteraction, reaction, or degradation during storage.

The flowchart 100 comprises a third step 106 comprising measuringelectrochemical data of the sample using an electrochemical cell. Theelectrochemical data may be potentiometric, coulometric, or voltammetricdata. For example a voltage may be varied over time and the resultingcurrent through the sample may be measured. The electrochemical cell maycomprise a plurality of electrodes. For example, there may be threeelectrodes: a working electrode, a second electrode, and a referenceelectrode. A portion of the sample containing the release agent maycontact each electrode. This detection of the measurement of the samplemay be either by destructive or non-destructive means. The temperatureof the sample may be actively controlled between 20 and 40 degreesCelsius while the step of measuring the electrochemical data isoccurring.

The flowchart 100 comprises a fourth step 108 comprising determining atotal serum bilirubin concentration of the sample using theelectrochemical data. The total serum bilirubin may be measured directlyor calculated by first determining the concentration of all bilirubinderivatives. Each analyte concentration may be determined from aspecific electrical energy measured in the electrochemical cell. Forexample, a bilirubin derivative may be known to oxidize near a specificvoltage, therefore the measured current near this voltage may correspondto the concentration of the specific analyte in the sample.

FIG. 2 depicts a flowchart 200 for a method for diagnosing a subjectbased on electrochemical detection of analytes. The method can comprisea first step 202 of providing a blood sample to be measured from thesubject, wherein the sample comprises both unbound bilirubin andbilirubin bound to albumin. A second step 204 comprises adding a releaseagent to the sample, the release agent configured to release the boundbilirubin from the albumin. A third step 206 comprises measuringelectrochemical data of the sample using an electrochemical cell. Afourth step 208 comprises determining concentrations of conjugatedbilirubin, unconjugated bilirubin, and albumin using the electrochemicaldata. A fifth step 210 comprises making a diagnosis of an illness forthe subject based on the determined concentrations of conjugatedbilirubin, unconjugated bilirubin, and albumin.

The method steps provided in 202, 204, 206, and 208 may use any of thetechniques or reagents described above for the method flowchart 100. Theillness diagnosed may be icterus. The diagnosis may provide aquantification of the severity of the illness. Similar to the step ofdiagnosing, the method may alternatively include a step of identifying ahuman subject as having increased risk of hyperbilirubinemia. Oncediagnosed or identified, the method may further comprise providing atreatment to the subject. The treatment may comprise phototherapy,intravenous immunoglobulin transfusions, or exchange transfusions. Oneexample of a phototherapy device is described in U.S. patent applicationSer. No. 15/143,227, which is incorporated herein by reference.

The illness diagnosed may alternatively be a prediction of stroke; aprediction of the development of Type II Diabetes; a prediction of thedevelopment of adverse cardiac events such as hyper-tension relatedheart-failure; a prediction of the development of Acute RespiratoryDistress Syndrome (ARDS) in sepsis; a diagnosis of decreased hepaticuptake; a diagnosis of decreased bilirubin conjugation (decreasedhepatic glucuronyl transferase) such as in Gilbert syndrome,Crigler-Najjar Type II, Crigler-Najjar Type I, and neonatal jaundice; adiagnosis of acquired transferase deficiency such as drug inhibition(chloramphenicol pregnanediol), breast milk jaundice, hepatocellulardisease like hepatitis and cirrhosis; a diagnosis of sepsis; a diagnosisof blood disorders such as hemolysis intra and extra vascular,erythroblastosis fetalis, and ineffective erythropoiesis; a diagnosis ofhereditary disorders due to impaired hepatic excretion such asDubin-Johnson syndrome, Rotor syndrome, and recurrent intrahepaticcholestasis; a diagnosis of acquired disorders due to impaired hepaticexcretion such as hepatocellular diseases like hepatitis and cirrhosis,drug induced cholestasis, alcohol liver disease, sepsis, postoperativestate, and biliary cirrhosis; or a diagnosis of disorders due toextrahepatic biliary obstruction such as gallstones, biliarymalformation, infection, malignancy, hemobilia, sclerosing cholangitis,and pancreatitis.

FIG. 3 depicts a system for electrochemical detection of analytes. Thesystem comprises a device 302 configured to receive a portion of acartridge 304, wherein the device comprises a receptacle 306 configuredto receive and be in electrical communication with a connector (notdepicted for clarity reasons) of the cartridge 304; a controller 308 inelectrical communication with the receptacle and configured to: controla potential on at least one of the electrodes; and receive electricalenergy and provide information regarding concentrations of analytespresent in a sample. In this depiction, some internal elements aredepicted as visible for clarity reasons. For example, a portion of a topsurface 310 of the cartridge 304 has been depicted as transparent.

Although not depicted in FIG. 3, the device 302 may have additionalcomponents configured to measure a temperature of a sample in thecartridge 304 and control the temperature of the sample to be maintainedbetween 20 and 40 degrees. For example, the device 302 may have anintegrated heater and thermometer. The cartridge top surface 310 may bemade of material with a thermal conductivity that allows the device 302to maintain a roughly uniform temperature at various zones of thecartridge 304. Temperature control may improve assay accuracy and allowthe device 302 to be used in ambient conditions where conventionalassays have traditionally been limited. The temperature may becontrolled relative to ambient temperature. The temperature of thesample may be automatically adjusted by the controller 308 to maintainvarious zones of the cartridge 302 at specific temperatures.

The device 302 may have additional components that improve its abilityto provide information regarding the concentrations of the analytes. Forexample, the device 302 may be configured to be hand-held. The device302 may have a graphical user interface, display, battery, wirelesscommunication module, one or more input ports, one or more output ports,or additional electrical components commonly used. The device may havecomponents for receiving instructional input from a user such as akeyboard, touchpad, or one or more buttons or switches. The device mayconnect to a cloud infrastructure for data storage and analytics. Thedevice may be configured to record and use the history of analyteconcentrations of a patient to allow trend monitoring of theconcentrations over time, thereby producing a nomogram. For example, thedevice may plot the hour specific TSB levels against gestational age(nomogram) in the subject. The rate of rise of bilirubin can help guidethe efficacy of the treatment to be administered for any form ofhyperbilirubinemia.

The receptacle may be a slot or hole of similar shape to the cartridge.The receptacle may be electrically connected to the controller and havecomponents configured to contact the connector of the cartridge andprovide electrical communication between the controller and thecartridge.

The cartridge 304 may have an external identifier 312. The externalidentifier may provide information regarding date of manufacturer orbatch number of the cartridge. This information may be used with atime-based algorithm to account for any cartridge aging effects. Thistime-based algorithm may be used to account for the errors caused bycartridge variability within batches and between batches by usingcalibration factors determined during the device's manufacturing.Further, any changes in the sensitivity of the device due to aging canbe calibrated for by a time-based aging model whose input may be the ageof the device since manufacture.

FIG. 4A depicts a perspective view of a cartridge 400 to be used in asystem for electrochemical detection of analytes. The cartridge 400generally comprises a receiving zone 402 configured to receive a sample,wherein the sample comprises bilirubin bound to albumin; a preparationzone 404 holding a release agent and configured to receive the samplefrom the receiving zone 402 and combine the sample with the releaseagent in order to release the bound bilirubin from the albumin; and asensing zone 406 having multiple electrodes and configured to receivethe sample from the preparation zone and provide electrical energy fromthe electrodes to a connector 408.

FIG. 4B depicts a top view of a cartridge 400 to be used with a systemfor electrochemical detection of analytes. The cartridge 400 has aninlet aperture 410 within the receiving zone, which may be tapered orwhose surface may be specifically functionalized to improve thetransmission of fluid into the preparation zone. For example, thesurface contacting the sample may be coated with hydrophilic adhesive,polyester, or polymethyl methacrylate (PMMA). This inlet aperture 410 isconnected to a fluid pathway 412 which defines a portion of thepreparation zone and fluidly connects the receiving zone to the sensingzone. The fluid pathway 412 comprises multiple filters 414. Chemicalagents 416 are also present within the fluid pathway 412. The sensingzone has a cavity 418 that has an air vent 420. The cavity 418 has threeelectrodes 422 which are electrically connected to three respectiveconnector electrodes 424 of the connector. The cartridge 400 has a body426 which serves to define the exterior shape as well as the variousinternal components.

The device and cartridge may use any method variation described hereinin order to achieve electrochemical detection of analytes. The analytesmay be total bilirubin, conjugated bilirubin, unconjugated bilirubin,and albumin. The inlet aperture may be configured to directly contact ablood sample, such as a blood drop.

Once a sample has been received by the receiving zone 402, it may travelvia capillary action through the fluid pathway of the preparation zoneto the sensing zone. Any surface of the fluid pathway that contacts thesample may be functionalized to assist the flow of blood. The surfacemay be specifically functionalized to allow the measurement of thesample to occur before the onset of phenomena such as blood coagulation.The fluid pathway may have dimensions that are designed to controlwhether flow is turbulent or laminar. The fluid pathway may be a channelor tube having a width of less than about 5 millimeters and a height ofless than about 1 millimeter. The fluid pathway dimensions may be sizedto reduce the total sample volume necessary for the detection, whilstremaining at a scale that allows for mass production. The length of thetube may be determined to allow for sufficient cooling and preparationof the sample.

As the sample travels through the preparation zone, it may be filteredand have chemical agents added. The filtering may be through sizeexclusion to remove gross debris and biochemical contaminants. Forexample, a size-exclusion membrane may be used to block any freehemoglobin reaching the sensing electrodes. Additionally, smallmolecules such as ascorbic acid may be blocked using membranes such ascellulose acetate. The filtering may be a functionalized surfaceconfigured to remove specific components from the sample.

The release agent and any additional agents may be added to the sampleeither in parallel or sequentially. The dissolution of these reagentscan be distinct or overlapping in respect to time. These agents may bedry formulated, lyophilized, or immobilized within films in order toimprove shelf life and stability of the system. The shelf life of thesystem may be longer than 30 days. The agents may also be printed alongthe channels using analogue/screen printing or digital printing methods.The timing of dissolution of these agents may be controlled through themanufacturing process where the print size and distribution of chemicalagent prints is optimized to ensure the correct timing of agentadditions.

The total serum bilirubin can be detected in the final sensing chamberby the use of a single or plurality of electrochemical assays. After ashort period of time, and upon adequate sample reaching the sensing zonean assay or measurement can take place upon the sample. The initiationof the measurement may be automated by a start condition which can be anelectrical signal produced by applying a voltage between electrodes, anda current that runs when the electrodes are shorted by the sample.Alternatively, the measurement can be initiated by the generation ofvoltage when the blood sample flows between electrodes. The controllermay provide this voltage by controlling the potential on at least one ofthe electrodes. A single sensing zone could be capable of measuring morethan one analyte or characteristic of the blood sample either inparallel or sequentially. The cavity of the sensing zone may have avolume of less than 10, 7, 4, or 2 microliters. There may be multiplesensing zones, each configured to provide alternative electricalinformation. Such multiple sensing zones may be connected to respectivemultiple preparation zones which differ in the concentrations orspecific chemical agents they hold.

The sensing zone may have multiple electrodes. There may specifically bethree electrodes. The electrodes may comprise carbon electrodes. Theelectrodes may comprise multi-walled carbon nanotubes, single-walledcarbon nanotubes, or graphene. The use of electrode materials such ascarbon can advantageously reduce the oxidation of interferences relativeto more catalytic materials such as platinum. Each of the electrodes inthe sensing zone may be electrically connected to respective connectorelectrodes located at the connector. The connector electrodes maycomprise any conductive material known in the art. The connector may beshaped to be inserted or attached to the receptacle of the device in amanner that allows electrical connection between the electrodes and thedevice.

Once the electrical energy is received at one or more of the electrodesand transferred to the device it may be used by the controller toprovide the concentrations of the analytes. Similar to the methodsdescribed herein, a voltage may be varied over time and the resultingcurrent through the sample may be measured. The electrical energyreceived may be calibrated relative to other signals including: ambienttemperature, sensing zone temperature, or ionic concentration, which maybe simultaneously measured. The measurements can be calibrated relativeto a number of other inputs including dissolved reagents and calibrationfactors integrated into the cartridge and determined during themanufacturing process. Further, the errors caused by sensor variabilitywithin batches and between batches may be removed both through devicecharacterization at the point of use and also by calibration factorsdetermined during the device's manufacturing.

The concentrations may be provided on a display of a device ortransferred to a remote system capable of monitoring the progression ofthe analyte concentrations over time; capable of conducting analytics toimprove prognosis of potential sequelae; capable of presenting theconcentrations in numerical and graphical formation; and/or capable ofexporting data and results in desired format. The body of the cartridgemay have a low flexural modulus. The body of the cartridge may comprisea polymer.

The system described herein provides several advantages over previousbilirubin detection systems. The system requires minimum interventionsby a user, therefore removing one of the biggest sources of inaccuracydue to user error when performing bilirubin measurements. In addition,by using electrochemical detection the system and methods provide fastermeasurements and has improved shelf life stability of reagents used forthe measurement. Further, the sample does not leave the device fromreception to final detection, therefore eliminating the risk of samplecontamination or sample loss. Similarly, concerns regardingcross-contamination between samples are eliminated as the cartridge maybe disposed of after measurement of a sample. Because the operation ofthe device is very rapid, the sample prevented from being degraded bylight exposure. Finally, the system is capable of offering the abovementioned advantages right at the patient bedside, or in remote clinicsthat do not have immediate access to chemistry analyzers.

The systems and methods described herein are capable of measuringbilirubin derivatives as well as albumin concentrations and cantherefore allow for improved accuracy when diagnosing neonatal jaundice.Quantifying the levels of these analytes can give practitioners aholistic perspective of the state of jaundice in a neonate or othersubject.

EXAMPLES

The following Examples are provided in order to demonstrate and furtherillustrate certain embodiments and aspects of the present disclosure andare not to be construed as limiting the scope of the disclosure.

Example 1

An experiment was performed to determine the effectiveness ofelectrochemical detection of albumin, conjugated bilirubin, unconjugatedbilirubin, and total serum bilirubin using a release agent such asbromophenol blue.

All electrochemical experiments were performed on screen-printed carbonelectrodes with an Ag/AgCl reference electrode in a 3-electrode mode ofoperation. Cyclic Voltammetry parameters were controlled via acomputational program; scan rate: 0.1 V/s, start potential: −0.5V,switch potential: 0.9V, end potential: −0.5V.

Bilirubin (mixed isomers), Fatty-acid free Human serum albumin,Bilirubin conjugated ditaurate disodium salt, Sodium hydroxide,Tris(hydroxymethyl)aminomethane, Hydrochloric acid, TetrabromophenolBlue were purchased from Sigma Aldrich, UK. Deionized water (resistivity18.2MΩ cm) was used in the preparation of solutions. Bilirubin wasdissolved in 0.05M sodium hydroxide to prepare 1 mM stock and gentlyvortexed till homogenously mixed. This stock solution was then dilutedusing 0.05 M Tris-HCl (pH 8.5) to the desired working concentration.Human serum albumin was prepared in 0.05M Tris-HCl (pH 8.5) and vortexedtill homogenously mixed. Bromophenol blue was prepared in 0.05M Tris-HCl(pH 8.5). Conjugated bilirubin was dissolved in 0.05M Tris-HCl (pH 8.5)and mixed till homogenous. All tubes containing bilirubin were protectedfrom light.

Regarding the detection of unbound unconjugated bilirubin, it wasdiluted to a physiologically relevant concentration (100 μM) andanalyzed by cyclic voltammetry. Unconjugated bilirubin exhibited a broadanodic peak E_(pa)=0.15V, demonstrating that unconjugated bilirubincould be directly oxidized on bare carbon electrodes in the solvent-freesystem. No cathodic peak was observed, thereby indicating irreversibleoxidation. Also, the peak at 0.15V was noticeably absent in second andthird scans. Without being bound by theory, it was suspected that themechanism of oxidation of bilirubin to biliverdin undergoes a loss oftwo electrons and two protons. Accordingly, we suspect that the peak at0.15V could be enhanced by using an electron-acceptor such as rutheniumhexamine or by increasing the concentration of a proton-acceptor such assodium hydroxide.

Consequently, a range of concentrations of bilirubin were tested toconfirm the anodic peak current is concentration dependent. A secondaryanodic peak was observed at 0.3V for higher concentrations which becamenoticeably distinct at concentrations of 50 μM and higher. Without beingbound by theory, it was suspected that the secondary anodic peaks can beattributed to the successive conversion of biliverdin to purpurin, thento choletelin, and further to subsequent products.

To further investigate the concentration to peak current correlation thescans were assessed for linearity. As per classical linearity criteria,acceptable linearity was defined as a correlation coefficient close to1, and y-intercept does not differ significantly from zero. The resultsshowed that at the concentration range of 1.5-10.0 mg/dL, peak heightcurrent is linear with concentration. The linearity study was thenextended to include physiological and pathophysiological ranges(10.0-170.0 mg/dL). As the oxidation of bilirubin involves the loss ofthe proton, more alkaline environments promote the oxidation process byremoving the proton and promoting the forward reaction. Therefore atbilirubin can be oxidized at lower potentials.

Regarding the detection of albumin-bound unconjugated bilirubin, withinhuman plasma, roughly 99.9% of unconjugated bilirubin is bound toalbumin due to the poor water solubility of bilirubin. Preparations ofphysiologically relevant concentrations of albumin and unconjugatedbilirubin were analyzed. It was found that the binding of unconjugatedbilirubin to albumin inhibited the direct electrochemical oxidation ofunconjugated bilirubin. The distinct unconjugated bilirubin peakE_(pa)=0.15V is attenuated when mixed with albumin and was found to beinstead replaced with peaks at 0.4V and 0.6V.

The inhibition of bilirubin oxidation by albumin needed to be addressedin order to accurately measure total serum bilirubin. Surfactants,caffeine, sodium benzoate and fatty acids are common solubilizingagents. These agents, in addition to alcohols were suspected of beingable to break the salt-linkage between unconjugated bilirubin andalbumin and were therefore examined for dissociation capabilities.However, the alcohol was found to interfere with the electro-oxidationprocess. Bromophenol blue was identified as a suitable agent which couldcompete with unconjugated bilirubin for the binding sites on albumin anddemonstrate compatibility with the electrochemical process. Thoughbromophenol blue is electrochemically active, its peak was found to bepresent at 0.64V, distinctly separate from the bilirubin peak at 0.15V.The binding of bromophenol blue to albumin was found to diminish thebromophenol blue peak at 0.64V. This is consistent with the effect ofalbumin on unconjugated bilirubin oxidation. At equal ratios of albuminto bromophenol blue or unconjugated bilirubin, the albumin can eliminateoxidation of binding partners, presenting only a single broad anodicpeak at 0.55V.

To better understand the electrochemical implications of thedisplacement effect, all three components—unconjugated bilirubin,albumin, and bromophenol blue—were mixed together at varying ratios andassessed by cyclic voltammetry. At equal concentration ratios, nodisplacement of unconjugated bilirubin was observed, indicated by theabsence of the unconjugated bilirubin peak. At ratio where thebromophenol blue is in excess, the liberation of unconjugated bilirubinwas evident by a characteristic peak at 0.15V. When the concentration ofbromophenol blue was increased two-fold, the peak current was 0.645 μA.However, when the bromophenol blue concentration was increasedthreefold, the peak current was reduced to 0.347 ρA and thecharacteristic bromophenol blue peak at 0.64V was predominant. Thepresence of the bromophenol blue peak indicated saturation of albuminbinding, resulting in unbound bromophenol blue which is available foroxidation. Next, the concentration of unconjugated bilirubin was doubledagainst the albumin and bromophenol blue; here the typical broad peak(E_(pa)=0.15V) of unconjugated bilirubin was present. The bromophenolblue-specific peak was absent, indicating all the bromophenol blue mayhave been participating in the displacement of bilirubin. These resultsprovide evidence that even at high concentrations of unconjugatedbilirubin, the higher binding affinity of bromophenol blue can displacebilirubin.

Regarding the measurement of conjugated bilirubin, this bilirubinderivative is the water-soluble form which has been glycosylated by theUDP enzyme within the liver. In clinical settings, the conjugatedbilirubin measurement is required to determine the albumin-boundbilirubin (unconjugated bilirubin) level from the total serum bilirubin.The cyclic voltammetry results of conjugated bilirubin is similar tothat of unconjugated bilirubin, consisting of an anodic peak at 0.15V.Like unconjugated bilirubin, a secondary anodic peak was found to bepresent at 0.3V indicating successive oxidation of biliverdin. However,unlike the scan of unconjugated bilirubin, the peak at 0.3V was distinctfrom the first peak. A third anodic peak at 0.44V was exhibitedspecifically by conjugated bilirubin. This third peak provides anopportunity to directly distinguish conjugated bilirubin fromunconjugated bilirubin without the need for a separate analysis.

A linearity study of conjugated bilirubin was then conducted tounderstand the concentration to peak height relationship across thephysiological concentration range of 0.0625 mg/dL to 25 mg/dL. All threepeaks were consistently present across all the concentrations tested,therefore conjugated bilirubin and unbound-, unconjugated-bilirubin areclearly distinguishable from one another. The results show that at theconcentration range of 0.0625 mg/dL to 20 mg/dL peak height current islinear with concentration.

The interaction of conjugated bilirubin and albumin was investigatedwith mixtures of conjugated bilirubin and albumin were prepared at equalconcentrations. As with unconjugated bilirubin, albumin complexes withconjugated bilirubin, albeit to a lesser degree, and hinders oxidationof bilirubin. This was demonstrated by the diminution of the peak at0.15V. However, the presence of a small peak at 0.15V does indicate thebinding affinity of conjugated bilirubin to albumin is weaker than thatof unbound bilirubin. Comparing the voltammetric results, it is clearthat some of the conjugated bilirubin did not bind albumin and isavailable for oxidation. As with the above results, the characteristicalbumin peak Epa=0.55V was observed.

These results indicate that to ensure the oxidation of conjugatedbilirubin, it will likely have to be isolated from albumin. As withunconjugated bilirubin, bromophenol blue was used a competitive bindingligand for the displacement of conjugated bilirubin. These threecomponents—conjugated bilirubin, albumin, and bromophenol blue—weremixed at equal concentrations and analyzed by cyclic voltammetry. At1:1:1 ratio, the bromophenol blue sufficiently displaced the conjugatedbilirubin as evidenced by the peak at 0.15V. Following the peak, thebroad scan obscures any successive peaks from either biliverdin, albuminor bromophenol blue.

The liberation of conjugated bilirubin and unconjugated bilirubindiffers in their distinctive voltammograms and required concentrationsof bromophenol blue. These differences could be used to differentiatebetween conjugated and unconjugated bilirubin in a single analysis.

Regarding the measurement of albumin, the results showed that albuminwas inherently electrochemically active, therefore a range ofphysiologically relevant concentrations were analyzed by cyclicvoltammetry to determine peak height to concentration correlation. Itwas found that the peak E_(pa)=0.55V on the first scan demonstratedlinearity with a concentration range of 1 g/dL to 5 g/dL. The linearitystudy was then extended to include a wider range 0.175 g/dL to 30 g/dL.The cyclic voltammogram of albumin demonstrates that across allconcentrations the broad peak at E_(pa)=0.6V is present; the peak ismore distinguishable at lower concentrations. Albumin maintained goodlinearity even at relatively high concentrations despite to broadeningof the peak. This albumin measurement may be used to supplement themeasurement of bilirubin and allow for a more accurate representation ofthe health of patients to be provided to clinicians.

The present disclosure has described one or more preferred embodiments,and it should be appreciated that many equivalents, alternatives,variations, and modifications, aside from those expressly stated, arepossible and within the scope of the invention.

1. A method for measuring bilirubin levels in a subject, the method comprising: providing a fluid sample to be measured from the subject to a microfluidic device, wherein the fluid sample comprises bilirubin bound to albumin; contacting the fluid sample and a release agent, the release agent configured to release the bound bilirubin from the albumin; measuring electrochemical data of the fluid sample using an electrochemical cell; and determining a total serum bilirubin concentration of the fluid sample using the electrochemical data.
 2. The method as recited in claim 1, wherein the release agent is dry formulated, lyophilized, or immobilized within a film.
 3. The method as recited in claim 1, wherein the fluid sample is an untreated blood sample of the subject.
 4. The method as recited in claim 1, wherein the release agent is cocamidopropyl sulfobetaine, 3-[3-Cholamidopropyl)-dimethylamminonio]-1-propanesulfonate, 3-[3-Cholamidopropyl)-dimethylamminonio]-2-hydroxy-1-propanesulfonate, cocamidopropyl betaine, caffeine, sodium benzoate, sodium acetate, ethylene glycol, hexadecanoic acid, (9Z)-octadec-9-enoic acid, haematin, a sulfonamide, salicylate, sodium dodecyl sulfate, or 4,4′-(1,1-dioxido-3H-2,1-benzoxathiole-3,3-diyl)bis(2,6-dibromophenol).
 5. The method of claim 1, wherein the volume of the fluid sample is less than 100 microliters.
 6. A method for measuring bilirubin levels in a subject, the method comprising: contacting a blood sample from the subject and a release agent, wherein the blood sample comprises bilirubin bound to albumin and the release agent is configured to release the bound bilirubin from the albumin; measuring electrochemical data of the blood sample using an electrochemical cell; and determining concentrations of conjugated bilirubin, unconjugated bilirubin, and total serum bilirubin using the electrochemical data.
 7. The method as recited in claim 6, wherein the release agent is dry formulated, lyophilized, or immobilized within a film.
 8. The method as recited in claim 6, wherein the release agent is cocamidopropyl sulfobetaine, 3-[3-Cholamidopropyl)-dimethylamminonio]-1-propanesulfonate, 3-[3-Cholamidopropyl)-dimethylamminonio]-2-hydroxy-1-propanesulfonate, cocamidopropyl betaine, caffeine, sodium benzoate, sodium acetate, ethylene glycol, hexadecanoic acid, (9Z)-octadec-9-enoic acid, haematin, a sulfonamide, salicylate, sodium dodecyl sulfate, or 4,4′-(1,1-dioxido-3H-2,1-benzoxathiole-3,3-diyl)bis(2,6-dibromophenol).
 9. The method as recited in claim 6, further comprising filtering the blood sample, wherein the filtering occurs prior to measuring the electrochemical data.
 10. The method as recited in claim 6, wherein the volume of the blood sample is less than 100 microliters.
 11. A method for measuring bilirubin levels in a subject, the method comprising: providing a blood sample to be measured from the subject, wherein the blood sample comprises bilirubin bound to albumin; contacting the blood sample and a release agent, the release agent configured to release the bound bilirubin from the albumin; measuring electrochemical data of the blood sample using an electrochemical cell; and determining concentrations of conjugated bilirubin, unconjugated bilirubin, total serum bilirubin, and albumin using the electrochemical data.
 12. The method as recited in claim 11, wherein the release agent is dry formulated, lyophilized, or immobilized within a film.
 13. The method as recited in claim 11, wherein the release agent is cocamidopropyl sulfobetaine, 3-[3-Cholamidopropyl)-dimethylamminonio]-1-propanesulfonate, 3-[3-Cholamidopropyl)-dimethylamminonio]-2-hydroxy-1-propanesulfonate, cocamidopropyl betaine, caffeine, sodium benzoate, sodium acetate, ethylene glycol, hexadecanoic acid, (9Z)-octadec-9-enoic acid, haematin, a sulfonamide, salicylate, sodium dodecyl sulfate, or 4,4′-(1,1-dioxido-3H-2,1-benzoxathiole-3,3-diyl)bis(2,6-dibromophenol).
 14. The method as recited in claim 13, wherein the release agent is 4,4′-(1,1-dioxido-3H-2,1-benzoxathiole-3,3-diyl)bis(2,6-dibromophenol).
 15. The method as recited in claim 11, wherein the electrochemical data is voltammetric data.
 16. The method as recited in claim 11, further comprising adding additional agents to the blood sample, wherein the addition of the agents occurs prior to measuring the electrochemical data.
 17. The method as recited in claim 16, wherein the additional agents are dry formulated, lyophilized, or immobilized within a film.
 18. The method as recited in claim 16, wherein the additional agents include at least one of a surfactant, buffer, salt, or second release agent.
 19. The method as recited in claim 11, wherein the temperature of the blood sample is actively controlled between 20 and 40 degrees Celsius while the step of measuring the electrochemical data is occurring.
 20. The method as recited in claim 11, wherein the volume of the blood sample is less than 100 microliters. 